1. Field of the Invention
The present invention relates to explosive devices, and particularly high pressure explosive devices that can be activated by electrical pulse or ignited by shock.
2. Background of the Art
Explosive devices are used in a wide range of industry and commerce. The very nature of explosives as they have been known for centuries makes them inherently dangerous. Attempts have been made to make them safer.
U.S. Pat. No. 6,540,175 describes an airborne countermine system comprising: at least one munitions dispenser element, a plurality of countermine munitions initially contained within said dispenser element, each of said munitions containing means for guiding said munitions to a predetermined coordinate location, and positioning the same for descent along a substantially vertical axis; means for initiating axial rotation to said countermines during vertical descent; each of said munitions containing a plurality of incendiary darts; means for opening said munitions during descent to radially distribute said darts using generated centrifugal force for individual vertical descent to a target area. The Patent describes high temperature incendiary fill to allow large amounts of chemical energy to be released over short periods of time. The dart high temperature incendiary fill employs an active ignition system to shock the fill up to reaction. High temperature incendiary fill candidates include titanium-boron-Teflon™ with CTBN as the binder, titanium-boron-Teflon™ with Viton®A as the binder, titanium-boron with ammonium perchlorate with Viton®A as the binder, aluminum potassium perchlorate with Viton®A as the binder and aluminum iron oxide with Viton®A as the binder. Viton®A is fluoropolymer elastomer that comes in many different variations of ingredients and properties. It includes copolymers of Tetrafluoroethylene, ethylene and ethers. These fills and high explosive fills may be employed in the countermine dart. The problem experienced with trying to package high temperature incendiary or explosive fills in small diameter countermine flechettes or darts is that it is difficult to ignite the fill in small calibers and maintain high velocity burn rates even in perforated fill designs. End-burners, as compared to perforated fill designs, burn at even slower burn rates and the ability to maintain the burn, due to heat transfer losses during the burn to the case of the countermine dart, is difficult. The use of an active ignition system overcomes all of these design issues allowing any one of a number of high temperature incendiary high explosive fills to be employed. The exact geometry of a high temperature incendiary countermine dart incorporates the cavity generating design features allowing hydrodynamic cavitation and terradynamic cavitation to be employed in high-speed penetration of soil and water, and an active ignition system to allow the dart fill to be shocked to reaction using a high temperature incendiary fill. The darts would also incorporate a staggered tail system to allow maximum number of darts to be packaged in the countermine munitions dispensing system.
U.S. Pat. No. 5,859,383 describes an innovative, safe, explosive device. The device has many potential fields of utility, including, but not limited to mining, oil exploration, seismology, and particularly to shaped charges. These shaped charges may be used as a well perforation system using energetic, electrically-activated reactive blends in place of high explosives. The reactive blends are highly impact inert and relatively thermally inert until activated. The proposed system requires no conventional explosives and it is environmentally benign. The system and its components can be shipped and transported easily with no concern for premature explosion. It also needs no special handling or packing. The performance in oil and gas well perforation can be expected to exceed that of conventional explosive techniques. The device is a shaped charge capable of projecting a mass which can perforate a solid object, said shaped charge comprising: a) a casing, b) an electrical connection means though said casing, c) a reactive mass within said casing, wherein said reactive mass is electrically conductive along its entire length, and said casing encloses said reactive mass, said reactive mass comprising an electrically conductive reactive material in association with an oxidizing agent. A preferred composition and method comprises an electrically conductive reactive mass comprises a distribution of aluminum metal and an oxidizing material which will oxidize said aluminum metal at a temperature of at least 1000 degree K. and activating said electrically conductive reactive mass with a pulsed electrical charge of at least 1 kJ/gram of aluminum in less than 20 microseconds.
U.S. Pat. No. 6,357,356 (Rim et al.) relates to an electric blasting device using aluminum foil, the objective of which lies in providing an economical and safe electric blasting device. In line with this objective; a portion of the outer conductor of the cable is removed, and the aluminum foil is inserted therein in order to electrically connect the inner and outer conductors. Between the aluminum foil and the inner conductor, water, an insulator, and a Teflon® polytetrafluoroethylene polymer tube are inserted. When pulse high-current is made to flow, the aluminum foil changes into the condition of plasma. The aluminum therefrom and water react to generate explosive power. The invention uses commercialized aluminum foil, in addition to having a short scattering distance of the fragments. It also allows a low-vibration blasting due to the short reaction time therein. U.S. Pat. No. 5,436,791 describes a perforating gun using an electrical safe arm device and a capacitor exploding foil initiator device. The capacitor exploding foil initiator device having a capacitor connected in parallel to a bleed resistor which are connected across an exploding foil initiator by an over-voltage gap switch. When a voltage of the capacitor reaches a breakdown voltage of the switch, the energy stored in the capacitor is discharged through the switch to the exploding foil initiator which initiates a detonator cord thereby detonating the shaped charges of the perforating gun.
U.S. Pat. No. 6,389,975 describes a switching circuit incorporating a Field Effect Transistor (FET), two series dual-tap gas tube surge arrestors, and high-voltage resistors as part of a high voltage switch of a fireset for initiating an exploding foil initiator (EFI). Until energizing the FET via a firing command, an operating voltage of 1000 V is held off by a combination of the surge arrestors and high-voltage resistors. Upon receipt of a firing signal, a 28 V source is used to energize the FET that, in turn, decreases the voltage across the one surge arrestor connected directly to ground and increases the voltage across the other surge arrestor. Upon reaching the breakdown voltage of the ionizable gas within the second surge arrestor, the gas ionizes, becomes electrically conductive, and dumps the second surge arrestor's voltage across the first surge arrestor. This causes the first surge arrestor to also break down. Both surge arrestors are now conducting. Thus, the 1000 V source is free to energize the remainder of the circuit, discharging a 0.20 micro(f) capacitor through the EFI. The breakdown of both arrestors occurs in nanoseconds, enabling an almost instantaneous initiation signal.
Explosive materials are known to be ignited in different ways. Typically, explosive materials have been ignited by flame ignition (e.g., fuses or ignition of a priming explosive), impact (which often ignites a priming explosive), chemical interaction (e.g., contact with a reactive or activating fluid), or electrical ignition. Electrical ignition may occur in two distinct ways, as by ignition of a priming material (e.g., electrically ignited blasting cap or priming material) or by direct energizing of an explosive mass by electrical power. U.S. Pat. No. 5,351,623 describes a device which safely simulates the loud noise and bright flash of light of an explosion. This device consists of an ordnance case which encloses a battery, an electronic control module, a charging circuit board, a bridge head, and a shock tube dusted with aluminum and an explosive. The electronic control module provides a time delay between initial activation of the device and the time when the device is ready to create a shock wave. Further, this electronic control module provides a central control for the electronics in the simulator. The charging circuit board uses the battery to charge a capacitor. Passing the voltage stored in the capacitor through the wires of the bridge head causes the explosive and the aluminum in the shock tube to react. This reaction produces a loud noise and bright white flash of light which simulates an explosion.
One other aspect of explosive devices which has been of great concern is the danger of premature detonation of the device or charge. The highly energetic release of the compositions used for providing explosions has usually been attended by a high degree of sensitivity or a low initiation threshold for the explosive reaction. Attempts at alternative energy sources for explosive devices have led in many directions, including the electrical ignition of metals in water. W. M. Lee, Metal/Water Chemical Reaction Coupled to a Pulsed Electrical Discharge, J. Appl. Phys. 69 (10), 15 May 1991 describes how capacitor stored energy is transferred to a wire conductor surrounded by a mixture of a reactive metal powder and water. The current explodes the small wire conductor and initiates a chemical reaction in the mixture. The chemical reaction in the mixture was direct reaction of the aluminum metal and the water as2Al+3H2O goes to Al2O3+3H2 to provide the energy for the investigation of explosive sources.
T. G. Theofanous, X. Chen and P. Di Piazza, Ignition of Aluminum Droplets Behind Shock Waves in Water, Phys. Fluids 6 (11), November 1994, pp. 3513-15 describes the reaction of gram quantities of molten aluminum with water under sustained pressure pulses of up to 40.8 Mpa in a hydrodynamic shock tube. Conditions are identified under which the thermal interaction develops into chemical ignition and total combustion events in the aluminum-water explosion.
Electrically triggered explosive devices are not per se novel. Electrical current has been used for more than one hundred years to ignite detonators, as for example with TNT or dynamite charges. Electrical signals are also used with modern explosive devices, including Explosive Bridge Wires and their membrane equivalents. Explosive bridge wires are thin wire(s) placed adjacent to an explosive charge. The wire(s) or membranes (exploding foil initiators) are very thin and have very low mass relative to the total mass of the charge (considerably less than 1% by weight). These films or wire(s) are placed adjacent to the explosive mass, and are electrically connected to a charge generator. The charge causes the wire to burst, creating a shock wave into and through the explosive material which initiates or enhances the explosive effect of the charge. The products of the reaction may react with the burst wire or foil in a redox reaction.
The nature of explosions and ignitions also varies according to different needs. For example, some ignitions (as described in U.S. Pat. No. 6,540,175) are seeking high temperature ignitions to initiate thermal reactions in proximity to the ignition of the incendiary fill. Other explosive materials seek to provide high pressures to impact and act on materials in close proximity to the blast. Each of these different techniques among ignition types and explosion effects requires differentiation among the materials used and the ignitions provided in the practice of the technologies. All of the above cited references are incorporated herein by reference for all of their teachings relating to the field of explosives, activators, detonators, electronics, materials and the like.